Rate dependency mechanism of crystalline rocks induced by impacts: Insights from grain-scale fracturing and micro heterogeneity

摘要

Rocks in nature contain a large number of defects and exhibit strong heterogeneity on grain scale. In this study, a novel three-dimensional multiscale method is proposed to investigate the dynamic behaviors and microfracturing in granitic rocks. In this numerical method, the heterogeneity in mineral components is reproduced by a series of a space filling Voronoi tessellations and particle filling in subgrains as computational nodal points to allow for transgranular fracturing. The rupture strength, temporal deformation fields, and failure patterns are compared with the experimental results to verify the reasonability and accuracy of the proposed method. Then, the underlying mechanism of grain-scale fracturing leading to fractal fracture surfaces, pervasively grain pulverization and deflection/penetration cracking model are discussed. It's shown that the fracture surface roughness is fractal dominated by two competitive mechanisms. The crack initiation time of intergranular tensile crack, transgranular tensile crack and shear cracks is gradually increased. The ratio of the number of tensile cracks exceeds 90% and that value of intergranular crack decreases from 56% to 33% as the strain rate increases. The appearance of multicracks activation and the transition from intergranular fracturing to transgranular fracturing is the underlying mechanism of rate dependency for granitic rocks.